1823.] Mr, DanielVs Meteorological Essays, 455 



We are next to imagine a sphere increasing in heat unequally 

 from the poles to the equator. In this case, the currents will set 

 as before, and at nearly the same altitude, but with unequal velo- 

 cities in different parts of their course. The height of the baro- 

 metric column at the surface will still be invariable ; if as has 

 been so far supposed, the heat be communicated to the atmo- 

 sphere immediately from the sphere, and be slowly transmitted 

 from the lower to the upper strata. But the influence of any 

 partial and temporary source of heat, the agency of which is 

 entirely confined to the higher regions of the atmosphere, will 

 produce a different train of phenomena. This local increase of 

 heat will augment disproportionately the elasticity of the supe- 

 rior strata, and will, therefore, disturb the regular flow of the 

 equatorial current. A fall of the barometer wherein this dis- 

 turbance takes place will be a necessary consequence of the 

 diminished density of the atmospheric column. 



The second part of Mr. Daniell's first essay is devoted to the 

 consideration of an atmosphere of pure unmixed aqueous vapour. 

 If the temperature of the sphere be supposed to be 32° on every 

 part of its surface, the experiments of Mr. Dalton have shown 

 that the elastic force of a vaporous atmosphere would at the 

 surface be equal to 0*2 of an inch of mercury. The density of 

 such an atmosphere would, from statical principles, decrease in 

 a geometrical progression for equal heights. But supposing the 

 temperature of the sphere to increase as before from the poles 

 to the equator, it is evident that on the principle of the cryopho- 

 rus, the elasticity of the whole vaporous atmosphere would be 

 determined by that at the lowest point. Mr. Daniell supposes, 

 therefore, that the passage of the vapour from one point to 

 another is mechanically retarded, so as to enable it to assume 

 the gradations due to the temperature of the subjacent part of 

 the sphere. The direction of the currents would, in this case, 

 be the reverse of that of a permanently elastic fluid, and they 

 would flow from the equator to the poles, instead of from the 

 poles to the equator. For increase of temperature augments 

 both the density and elasticity of aqueous vapour, when in con- 

 tact with water ; whereas in a free atmosphere of a permanently 

 elastic fluid, increased elasticity is always accompanied by dimi- 

 nished density. At different elevations, the aqueous vapour 

 would naturally assume the temperature due to its density. But 

 if the heat of the higher strata be supposed to be diminished by 

 any cause at a greater rate than is due to this natural gradation, 

 a partial condensation must necessarily ensue. 



Under the third division of Essay I. Mr. Daniell proceeds to 

 inquire into the relations of a compound atmosphere, formed by 

 the combination of aqueous vapour with a permanently elastic 

 fluid. The basis of this investigation, as of the two former, is 

 founded on the discoveries of Mr. Dalton. That philosopher 

 (in his " New System," p. 150) was the first to reject the com- 



